THE SELECTION OF GENETIC RECOMBINATIONS WITH BACTERIAL GROWTH INHIBITORS

Abstract

demonstrated with a nutritional selective method (Tatum and Lederberg, 1947; Lederberg, 1947). A variety of mutants of K-12 were obtained with growth factor deficiencies that prevented growth in a synthetic agar medium. Recombinations between different mutant strains in mixed culture were selected by inoculating washed suspensions into synthetic agar plates. The colonies that appeared 24 to 48 hours later represented cells that had exchanged genetic factors so that they possessed the full complement needed to synthesize all of their own growth substances. To detect such recombinants, selection is essential, as they make up only about one one-millionth of the mixed bacterial culture. In principle, other selective agents besides nutritionally deficient medium could be used to detect recombinants. Bacterial growth inhibitors should lend themselves to this application, particularly as inhibitor-resistant mutants can be obtained more readily than nutritional mutants in many organisms. The method would consist first of isolating two mutants, each resistant to one inhibitor, but sensitive to the other. Then, recombinants resistant to both inhibitors would be